The invention relates to an apparatus for extracorporeal blood treatment, and a method for readying the apparatus.
Specifically, though not exclusively, the invention can be usefully applied in verification of a correct readying of a medical apparatus using an extracorporeal blood circuit, such as for example a hemodialysis or hemo(dia)filtration apparatus.
An apparatus for extracorporeal blood treatment includes a stage, preliminary to treatment true and proper, in which the disposable extracorporeal blood circuit, is coupled to the treatment control monitor (for example a dialysis monitor). This stage, which is performed before connecting up the extracorporeal blood circuit to the patient, includes connection of the blood transport lines (in general an arterial line for blood removal from the patient, and a venous line for blood return to the patient) to a membrane device for blood treatment (for example a hemodialyser in a case of hemodialysis), which in turn is connected up to a treatment fluid supply circuit (for example a dialysis fluid) and to a used treatment fluid discharge circuit. The membrane device for blood treatment comprises a semi-permeable membrane which divides a blood compartment, connected to the blood transport lines, and a fluid compartment, connected to the above-mentioned supply and discharge circuits. The blood transport lines are further coupled to a sensor and actuator system equipped on the dialysis monitor, which system normally comprises means for blood circulation (for example a blood pump, usually peristaltic), pressure sensors, an air bubble sensor, one or more circuit blocking clamps, etc. Before connection of the extracorporeal blood circuit to the patient's vascular system, a priming stage is usually performed of the blood transport lines and the blood treatment device, which are filled with a priming liquid (usually an isotonic saline solution or another patient-isotonic liquid) which performs the function of expelling air, filling and rinsing.
One of the drawbacks in the prior art derives from the fact that usually the dialysis monitor can be predisposed to receive various types of extracorporeal circuits suitable for effecting different treatments on different patients; in particular the monitor can serve for treatment of adult patients and children. In the two cases, the parameters regulating the treatment, which are preset by the operator, are very different. For example, the blood flow rate is usually lower when a child is to be treated; also the weight loss and the anticoagulant flow rate are lower. Similarly, the extracorporeal blood circuits used are of different types, especially as regards the dimensions of the components of the circuit. For example, the diameter of the blood transport lines is usually smaller in a pediatric extracorporeal circuit.
A grave risk for the health of a patient arises if a circuit suitable for one type of treatment (for example a blood line for an adult) is readied on a dialysis monitor set with parameters suitable for a different type of treatment (for example a treatment for a child). To reduce the risk a security system is predisposed, provided with means for recognising the type of dialysis circuit which is coupled to the monitor. The known means of recognition comprise an optical reading system which reads an identifying signal, for example a bar code, applied to the extracorporeal circuit. The known security systems for recognition of the extracorporeal circuit in an apparatus for extracorporeal blood treatment are liable to improvement in terms of both cost and reliability.
Also known is monitoring the flow resistance in a fluid transport tube, in which an increase in the flow resistance, signalled by an increase in pressure in the tube, provides an indication of the presence of an occlusion in the tube.
U.S. Pat. No. 4,898,576 describes a method which instead of simply waiting for a pressure increase in the fluid transport line, causes a controlled variation in the flow along the line, then measures the pressure variation due to the flow variation, and thus determines the flow resistance offered by the transport line on the basis of the above-mentioned variations.
EP 387724 describes a vascular infusion apparatus provided with an infusion line on which a peristaltic infusion pump and a pressure sensor downstream of the pump operate. A controller is programmed to increase the pump velocity periodically and for a brief time so that at each perturbation of the system a determined volume of liquid is added to the normal equilibrium flow. The pressure is measured and the pressure change with respect to the equilibrium flow, i.e. the change in pressure due to the perturbation, is integrated and divided by the volume of added liquid during the perturbation so as to determine the resistance to the fluid flow. By considering also the duration of the perturbation, the compliance of the infusion line can be determined.
EP 784493 describes two monitoring methods of the flow resistance in an infusion apparatus provided with a peristaltic pump, the first used for high flow and the second for low flow. In the first, high-flow method, the pressure is calculated at two different flow rates and the processor calculates the resistance as being equal to the pressure change divided by the flow rate change. The second method, for low flow-rates, involves pumping an intermittent flow and measuring the corresponding pressure signal. The pressures in the absence of flow are subtracted from those in the presence of flow. Then the pressure differences thus obtained are processed using a mathematical model in order to obtain the tube resistance.
U.S. Pat. No. 5,213,573 describes a method for monitoring the appropriate functioning of an IV administration set, in which an infusion pump is alternatingly commanded in order to remove a predetermined volume of fluid from a patient at a first pressure during a predetermined interval of time, and in order to infuse a predetermined volume of fluid to the patient at a second pressure in a second time interval. An eventual presence of an anomalous flow through the IV administration set is revealed by a comparison between the above-mentioned pressures. The anomalous flow can be caused, for example, by an incorrect positioning of the needle in the vascular access, such as to cause infiltration into the patient's tissue.
EP 458910 describes an apparatus provided with a peristaltic pump and a device for measuring the diameter of a transport tube associated to the pump, and which consequently regulates the pump velocity in accordance with a possible changing of the tube diameter in order to maintain the infusion flow rate at a constant level.
The prior art further comprises various systems for determining the actual blood flow rate generated by a peristaltic pump in an extracorporeal blood transport line, such as for example in WO 03/055542, which uses a memorised predetermined calibration function, the principal values of which are the angular velocity of the pump, the arterial pressure upstream of the pump, the effective blood flow rate and the work time since start of treatment of the tract of line coupled to the pump. Calibration functions can be used that also contain the following variables: the geometric characteristic of the vascular access in which the extracorporeal circuit removes blood from the patient, the length of the tract of arterial line upstream of the peristaltic pump, the pressure downstream of the peristaltic pump, the temperature of the extracorporeal circuit and the value of the blood hematocrit of the patient. From the values measured during the course of the treatment of the above variables, by use of the calibration function a precise value for the effective flow rate of the blood flow can be calculated.